Mesa Falls Tuff

Mesa Falls Tuff is a volcanic rock formation in eastern Idaho that stretches hundreds of meters thick and appears across the Island Park region, the lower slopes of the Centennial Mountains, and the southern Madison Range. The rock is layered in different sections, each showing signs of different volcanic processes and preserving details about the area's geological past.

This formation resulted from a massive volcanic eruption roughly 1.3 million years ago, when enormous amounts of material were expelled during the second cycle of volcanic activity in the Yellowstone region. The eruption reshaped the landscape and created the rock layers that scientists still examine today.

Scientists from the U.S. Geological Survey conduct regular research at Mesa Falls Tuff to understand volcanic patterns and regional geological development.

The best spot to view this formation is along U.S. Highway 20, north of Ashton, where the layered rock is clearly visible from roadside locations. Sturdy footwear is recommended since the terrain is uneven and rocky.

The layers reveal an unusual pattern: at the bottom lies a distinct band of air-fall pumice, followed by ash-flow tuff containing large feldspar crystals. This striking arrangement helps geologists identify different phases of a single eruption event.